The importance of flavor in leptogenesis

Abstract

We study leptogenesis from the out-of-equilibrium decays of the lightest heavy neutrino N 1 in the medium (low) temperature regime, T < ∼ 10 12 GeV (10 10 GeV), where the rates of processes mediated by the τ (and µ) Yukawa coupling are non negligible, implying that the effects of lepton flavors must be taken into account. We find important quantitative and qualitative differences with respect to the case where flavor effects are ignored: (i) The cosmic baryon asymmetry can be enhanced by up to one order of magnitude; (ii) The sign of the asymmetry can be opposite to what one would predict from the sign of the total lepton asymmetry ǫ 1 ; (iii) Successful leptogenesis is possible even with ǫ 1 = 0. * enrico.nardi@lnf.infn.it † yosef.nir@weizmann.ac.il

Towards constraints on the SUSY seesaw from flavour-dependent leptogenesis

“…As recently pointed out [10,11,12], flavour can have a strong impact in baryogenesis via thermal leptogenesis. The effects are manifest not only in the flavour-dependent CP asymmetries, but also in the flavour-dependence of scattering processes in the thermal bath, which can destroy a previously produced asymmetry.…”

Minimal lepton flavour violation and leptogenesis with exclusively low-energy CP violation

“…Recent studies [1][2][3][4][5][6][7] pointed out that flavour effects in the Boltzmann equations can be relevant for the generation of the baryon asymmetry of the universe and that when flavours are treated specifically, CP violation at high energies is no longer a necessary requirement of successful leptogenesis [4,[7][8][9][10].…”

“…This however does not universally hold when ranges of the Majorana scale are considered in which flavour effects play a role [4,[7][8][9][10]. These analyses were performed for hierarchical [8][9][10], for two quasi-degenerate [9] and for three quasi-degenerate heavy right-handed Majorana neutrinos [7].…”

“…While the common belief in the past years was that distinguishing flavours in the Boltzmann equations is not necessary, it turned out recently [1][2][3][4][5][6][7] that flavour effects can be relevant for the generation of the baryon asymmetry of the universe (BAU).…”

“…There have been several investigations recently of the importance of flavour effects [1][2][3][4][5][6][7]. Below some temperature, the interactions associated with the µ and τ charged lepton Yukawa couplings are much faster than the expansion of the universe and so are in equilibrium.…”